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block: blk-merge: fast-clone bio when splitting rw bios

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biovecs has become immutable since v3.13, so it isn't necessary
to allocate biovecs for the new cloned bios, then we can save
one extra biovecs allocation/copy, and the allocation is often
not fixed-length and a bit more expensive.

For example, if the 'max_sectors_kb' of null blk's queue is set
as 16(32 sectors) via sysfs just for making more splits, this patch
can increase throught about ~70% in the sequential read test over
null_blk(direct io, bs: 1M).

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Ming Lin <ming.l@ssi.samsung.com>
Cc: Dongsu Park <dpark@posteo.net>
Signed-off-by: Ming Lei <ming.lei@canonical.com>

This fixes a performance regression introduced by commit 54efd50bfd,
and allows us to take full advantage of the fact that we have immutable
bio_vecs. Hand applied, as it rejected violently with commit
5014c311ba.

Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Ming Lei 2015-09-17 09:58:38 -06:00 committed by Jens Axboe
parent 6fe810bda0
commit 52cc6eead9
1 changed files with 4 additions and 15 deletions
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19
block/blk-merge.c
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@ -66,15 +66,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
struct bio *bio,
struct bio_set *bs)
{
struct bio *split;
struct bio_vec bv, bvprv, *bvprvp = NULL;
struct bvec_iter iter;
unsigned seg_size = 0, nsegs = 0, sectors = 0;
bio_for_each_segment(bv, bio, iter) {
sectors += bv.bv_len >> 9;
if (sectors > queue_max_sectors(q))
if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q))
goto split;
/*
@ -95,6 +92,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
seg_size += bv.bv_len;
bvprv = bv;
bvprvp = &bv;
sectors += bv.bv_len >> 9;
continue;
}
new_segment:
@ -105,21 +103,12 @@ new_segment:
bvprv = bv;
bvprvp = &bv;
seg_size = bv.bv_len;
sectors += bv.bv_len >> 9;
}
return NULL;
split:
split = bio_clone_bioset(bio, GFP_NOIO, bs);
split->bi_iter.bi_size -= iter.bi_size;
bio->bi_iter = iter;
if (bio_integrity(bio)) {
bio_integrity_advance(bio, split->bi_iter.bi_size);
bio_integrity_trim(split, 0, bio_sectors(split));
}
return split;
return bio_split(bio, sectors, GFP_NOIO, bs);
}
void blk_queue_split(struct request_queue *q, struct bio **bio,